Breathing through the nose also allows the hairs to properly filter the air and the blood vessels/mucous membrane to properly moisten the air and get it to the right temperature. It prevents respiratory infection and bronchitis.

The lungs' expansion and contraction is controlled by the movement of the intercostal muscles and the diaphragm. Of these, the diaphragm is by far the more powerful and can be controlled to a much greater degree by engaging the stomach muscles. This is why breathing from the core brings in so much energy; it means that you're pulling in more oxygen / expelling more carbon dioxide per breath and not wearing the chest out whilst doing so. It tones the stomach, too.

More amazingly you can dramatically increase your cardiovascular endurance through nose breathing.

Choose an exercise eg running or cycling and only breathe through your nose. When you get to a point where you feel you need to breathe through your mouth then SLOW DOWN to a point where you need only breathe through your nose again. Gradually you will find you can go faster and faster nose breathing only and more quickly than you think you will be exercising at the same intensity you used to with a major difference - your perceived exertion will be much lower ie you will find that you can run at your old speed with virtually no apparent effort. Instead of puffing away it will seem like a walk in the park.

The lungs' expansion and contraction is controlled by the movement of the intercostal muscles and the diaphragm. Of these, the diaphragm is by far the more powerful and can be controlled to a much greater degree by engaging the stomach muscles. This is why breathing from the core brings in so much energy; it means that you're pulling in more oxygen / expelling more carbon dioxide per breath and not wearing the chest out whilst doing so. It tones the stomach, too.

My point exactly-Guinness? Fond memories of the pub called the Shepards Inn (I think) a few blocks west of the British Museum. I envy anyone who gets to live in London.